1. Field of the Invention
The present invention provides environmentally safe viscous well treating fluids and methods of treating subterranean zones therewith.
2. Description of the Prior Art
Viscous treating fluids are used in a variety of operations and treatments in oil and gas wells. Such operations and treatments include, but are not limited to, well completion operations and production stimulation treatments.
An example of a well completion operation involving the use of viscous treating fluids is gravel packing. In gravel packing operations, solid gravel particles such as graded sand are carried to a subterranean zone in which a gravel pack is to be placed by a viscous gelled treating fluid. That is, the gravel is suspended in the viscous fluid at the surface and carried to the subterranean zone in which the gravel pack is to be placed. Once the gravel is placed in the zone, the viscous gelled treating fluid is broken (the viscosity is reduced) and recovered. The gravel pack produced functions as a filter to separate formation solids from produced fluids while permitting the produced fluids to flow into and through the well bore.
An example of a production stimulation treatment utilizing a viscous treating fluid is hydraulic fracturing. That is, a viscous gelled treating fluid, referred to in the art as a fracturing fluid, is pumped through the well bore into a subterranean zone to be stimulated at a rate and pressure such that fractures are formed and extended into the subterranean zone. The fracturing fluid also carries particulate proppant material, e.g., graded sand, into the fractures. The proppant material is suspended in the viscous fracturing fluid so that the proppant material is deposited in the fractures when the viscous fracturing fluid is broken and recovered. The proppant material functions to prevent the formed fractures from closing whereby conductive channels are formed through which produced fluids can flow to the well bore. The usual candidates for fracturing or other stimulation procedures are production wells completed in oil and/or gas containing formations. However, injection wells used in secondary or tertiary recovery operations, for example, for the injection of water and gas, may also be fractured in order to facilitate the injection of the fluid into subterranean formations.
After the viscous fracturing fluid has been pumped into a subterranean zone in a formation and fracturing of the zone has taken place, the fracturing fluid is removed from the formation to allow produced hydrocarbons to flow through the created fractures. Generally, the removal of the viscous fracturing fluid is accomplished by converting the fracturing fluid into a low viscosity fluid. This has been accomplished by adding a delayed breaker, i.e., a viscosity reducing agent, to the fracturing fluid prior to pumping it into the subterranean zone.
The viscous treating fluids utilized heretofore have predominately been water-based fluids containing a gelling agent comprised of a polysaccharide such as guar gum. Guar and its derivatives such as hydroxypropylguar are economical water soluble polymers that can be used to create high viscosity in an aqueous fluid and are readily cross-linked which further increases the viscosity of the fluid. While the use of gelled and cross-linked polysaccharide treating fluids has been highly successful, some of the components in the treating fluids, particularly the delayed cross-link delinkers or breakers utilized have not been environmentally benign. Thus, there are needs for improved subterranean zone treating fluids and methods whereby the treating fluids include environmentally benign components.